Determinants of radiation dose to immune cells during breast radiotherapy.

BACKGROUND: The immune system has been identified as an organ at risk in esophageal and lung cancers. However, the dosimetric impact of radiotherapy on immune system exposure in patients treated for breast cancer has never been studied. METHODS: A monocentric retrospective dosimetric study included 163 patients treated at the Institut Curie (Paris, France) between 2010 and 2016 with locoregional helical tomotherapy after conservative surgery or total mastectomy. The effective dose to the immune system (EDIC) was calculated based on diverse dosimetric parameters. The clinical and volumetric determinants of EDIC in adjuvant radiotherapy of breast cancer were analyzed. RESULTS: The median EDIC for the population was 4.23 Gy, ranging from 1.82 to 6.19 Gy. Right-sided radiotherapy and regional lymph node irradiation were associated with significantly higher EDIC in univariate (4.38 Gy vs. 3.94 Gy, p < 0.01, and 4.27 Gy vs. 3.44 Gy, p < 0.01, respectively) and multivariate analyses (p < 0.01 and p < 0.01). Liver overexposure was the main contributor to EDIC increase in right-sided breast cancer patients (+0.38 Gy [95%CI: +0.30; +0.46]), while the integral total dose increase was the main contributor to EDIC increase in cases of regional node irradiation (+0.63 Gy [95%CI: +0.42; +0.85]). CONCLUSION: The EDIC score during adjuvant radiotherapy after breast cancer was statistically significantly higher in the case of right-sided radiotherapy and regional lymph node irradiation. Liver irradiation is the main contributor to immune system exposure in adjuvant irradiation of right-sided breast cancer. Populations in which an association between EDIC and survival would exist have yet to be identified but could potentially include patients treated for triple-negative breast cancer with a poor response to neoadjuvant chemoimmunotherapy.

Nutrition outcomes and treatment toxicities in patients with head and neck cancer receiving helical intensity-modulated radiotherapy.

BACKGROUND: Helical intensity-modulated radiotherapy (H-IMRT) provides excellent limitation of dose to tissues not requiring treatment, although acute toxicity still occurs. The present study aimed to determine how treatment-related acute toxicities affect nutrition outcomes in patients with head and neck cancer. METHODS: A prospective observational study was conducted in 194 patients undergoing curative intent H-IMRT with or without other treatment modalities. Weight outcomes (kg) and acute toxicity and dysphagia data were collected during treatment using Common Toxicity Criteria for Adverse Effects (CTCAE), version 4.0. RESULTS: Significant weight loss (> 10%) was observed in 30% of high nutritional risk patients and 7% of low nutritional risk patients. Nausea, adjusted for baseline dysphagia, in high nutritional risk patients and nausea, dysphagia and pharyngeal mucositis in low nutritional risk patients were significant factors in explaining the percentage loss in baseline weight to treatment completion. CONCLUSIONS: Significant weight loss remains an issue during treatment, despite improvements in radiotherapy technology and high-level multidisciplinary care.

Does intensity-modulated radiation therapy by helical tomotherapy for prostate cancer increase the subsequent risk of bladder cancer? A propensity score-matched analysis.

OBJECTIVES: This study aimed to evaluate the risk of bladder cancer after intensity-modulated radiation therapy (IMRT) using helical tomotherapy for prostate cancer in comparison to the risk post-radical prostatectomy (RP) using propensity score-matched analysis and to assess the risk factors for bladder cancer. METHODS: This retrospective study included 2067 patients with non-metastatic prostate cancer treated at our institution between June 2007 and December 2016. Of these, 1547 patients were treated with IMRT and 520 underwent RP. The propensity scores were calculated using age, National Comprehensive Cancer Network risk classification, prostate volume, Brinkman index, and follow-up time as matched covariates. A propensity score-matched patient cohort (n = 718; IMRT: 359, RP: 359) was created, and the risk of bladder cancer after treatment was compared. RESULTS: In total, bladder cancer was detected in 33 patients. Five patients in the IMRT group and one in the RP group died of bladder cancer. In the propensity score-matched analysis, the 5-year bladder cancer-free survival rate was significantly lower in the IMRT group than in the RP group (91.7% and 96.2%, respectively; p < 0.001). Multivariate analysis revealed that IMRT and the Brinkman index were the risk factors for bladder cancer in this cohort (odds ratio = 5.085, 95% confidence interval = 1.436-18.008, p = 0.012 and odds ratio = 1.001, 95% confidence interval = 1.000-1.001, p = 0.010, respectively). CONCLUSIONS: IMRT for prostate cancer using helical tomotherapy increases the subsequent risk of bladder cancer compared with RP and is an independent risk factor for bladder cancer similar to smoking.

Investigation on the accuracy of field widths and the quantitative relationship with energy variations for dynamic jaws helical tomotherapy.

BACKGROUND AND PURPOSE: TomoEDGE is an advanced technology for TomoTherapy treatment delivery by introducing a sliding-window dynamic jaw motion. The front and back jaws move independently at the start and end of a target volume along the longitudinal couch direction to reduce the undesired dose to the normal tissues. The accuracy of field width is essential to treatment delivery in this regard. The purpose of this work was to analyze the performance of dynamic jaws on helical tomotherapy and investigate the relationship with energy variation. METHODS: The Tomotherapy-Quality-Assurance (TQA) Dynamic Field Width procedure was performed monthly across three tomotherapy machines. All field widths were analyzed, especially the FWHM of the 10 mm field width. Field width measurements were compared with the ratio of Percentage Depth Dose at 20 and 10 cm to render the value of correlation. Changes in beam FWHM and energy were further discussed. Two-year data were collected for this purpose. RESULTS: On average, measured field widths in each unit agreed within 1% tolerance recommendation stated. The average absolute difference between reference and measured FWs in each unit was approximately 0.07 mm. An increase of 1.5% in the FW of the 10 mm nominal beam width was correlated with a 1% increase in PDD20,10 ratio, implying a positive correlation between the two factors (p < 0.002). CONCLUSIONS: A positive correlation between nominal 10 mm FW and PDD20,10 was observed. In the case that the PDD20,10 marginally passes the QA tests, users are recommended to consider further verification on Dynamic Jaws to ensure the smallest field width to be within tolerance, which is essential to maintain effective treatment in TomoEDGE system. Since the regression of this study was a single-factor model, other confounding factors such as the focal spot size of linear accelerator should also be considered when evaluating the machine status.

Dosimetric comparison of helical tomotherapy and volumetric modulated arc therapy in hippocampal avoidance whole-brain radiotherapy.

OBJECTIVE: This study aimed to discuss the dosimetric advantages of helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) technology in hippocampal avoidance whole-brain radiotherapy and provide references for clinical selection of ideal radiotherapy technology. METHODS: A total of 20 patients with hippocampal avoidance whole-brain radiotherapy were chosen randomly. Computed tomography (CT) and MRI scanning images were input into the treatment planning system (TPS). After the CT and enhanced magnetic resonance T1 weighted images were fused and registered, the same radiation therapy physician was invited to outline the tumor target volume. PTV-HS refers to the whole brain subtracted by 5 mm outward expansion of the hippocampus (HP). The prescribed dose was 30 Gy/10 fractions. HT and VMAT plans were designed for each patient in accordance with PTV. Under the premise that the 95% isodose curve covers the PTV, dose-volume histogram was applied to evaluate the PTV, conformal index (CI), heterogeneity index (HI), maximum dose (Dmax), mean dose (Dmean), minimum dose (Dmin) and absorbed doses of organs at risk (OARs) in HT and VMAT plans. Paired t-test was performed to compare the differences between two radiation therapy plans, and p  <  0.05 was considered statistically significant. RESULTS: These two plans had no significant difference in PTV-HS (max, min, and mean). However, the HI and CI of the HT plan were significantly better than those of the VMAT plan, showing statistically significant difference (p < 0.05). The HT plan was significantly superior to the VMAT plan in terms of the Dmax, Dmin, and Dmean of HP, left and right eye lens, left and right eye, and spinal cord, showing statistically significant difference (p < 0.05). The HT plan was also better than the VMAT plan in terms of the Dmax of the left optic nerve. However, the two plans showed no obvious differences in terms of the absorbed doses of the right optic nerve and brainstem, without statistical significance. CONCLUSIONS: Compared with the VMAT plan of hippocampal avoidance, HT technology has significant dosimetric advantages. HT plans significantly decreased the radiation dose and radiation volume of OARs surrounding the target area (e.g., surrounding eye lens and eye, especially hippocampal avoidance area) while increasing the CI and HI of PTV dose in whole brain radiotherapy (WBRT) greatly, thus enabling the decrease in the incidence rate of radioactive nerve function impairment.

Dosimetric evaluation in Helical TomoTherapy for lung SBRT using Monte Carlo-based independent dose verification software.

PURPOSE: To elucidate the dosimetric errors caused by a model-based algorithm in lung stereotactic body radiation therapy (SBRT) with Helical TomoTherapy (HT) using Monte Carlo (MC)-based dose verification software. METHODS: For 38 plans of lung SBRT, the dose calculation accuracy of a treatment planning system (TPS) of HT was compared with the results of DoseCHECK, the commercial MC-based independent verification software. The following indices were extracted to evaluate the correlation of dosimetric errors: (1) target volume, (2) average computed tomography (CT) value of the planning target volume (PTV) margin, and (3) average CT value of surrounding 2-mm area of the PTV (PTV ring). Receiver operating characteristic (ROC) analyses determined the threshold for 5% of differences in PTV D95%. Then, the 38 plans were classified into two groups using the cutoff values of ROC analysis for these three indices. Dosimetric differences between groups were statistically compared using the Mann-Whitney U test. RESULTS: TPS of HT overestimated by more than 5% in the PTV D95% in 16 of 38 plans. The PTV ring showed the strongest correlation with dosimetric differences. The cutoff value for the target volume, the PTV margin, and the PTV ring was 14.7 cc, -754 HU, and -708 HU, respectively. The area under the curve (AUC) for the target volume, the PTV margin, and the PTV ring were 0.835, 0.878, and 0.932, respectively. Dosimetric errors more than 5% were observed when the PTV volume was less than 15 cc or when the CT value around the target was less than -700 HU. CONCLUSION: The TPS of HT might overestimate the PTV dose by more than 5% if any the three indices in this study were below threshold. Therefore, independent verification with an MC-based algorithm should be strongly recommended for lung SBRT in HT.

Helical TomoTherapy Total Lymphoid Irradiation and Hematopoietic Cell Transplantation for Kidney Transplant Tolerance in Rhesus Macaques.

Development of a post-transplant kidney transplant tolerance induction protocol involving a novel total lymphoid irradiation (TLI) conditioning method in a rhesus macaque model is described. We examined the feasibility of acheiving tolerance to MHC 1-haplotype matched kidney transplants by establishing a mixed chimeric state with infusion of donor hematopoietic cells (HC) using TomoTherapy TLI. The chimeric state was hypothesized to permit the elimination of all immunosuppressive (IS) medications while preserving allograft function long-term without development of graft-versus-host-disease (GVHD) or rejection. An experimental group of 11 renal transplant recipients received the tolerance induction protocol and outcomes were compared to a control group (n = 7) that received the same conditioning but without donor HC infusion. Development of mixed chimerism and operational tolerance was accomplished in two recipients in the experimental group. Both recipients were withdrawn from all IS and continued to maintain normal renal allograft function for 4 years without rejection or GVHD. None of the animals in the control group achieved tolerance when IS was eliminated. This novel experimental model demonstrated the feasibility for inducing of long-term operational tolerance when mixed chimerism is achieved using a TLI post-transplant conditioning protocol in 1-haplotype matched non-human primate recipients of combined kidney and HC transplantation.

Investigation of total skin helical tomotherapy using a 3D-printed total skin bolus.

OBJECTIVE: To investigate the effectiveness of using a 3D-printed total skin bolus in total skin helical tomotherapy for the treatment of mycosis fungoides. MATERIALS AND METHODS: A 65-year-old female patient with a 3-year history of mycosis fungoides underwent treatment using an in-house desktop fused deposition modelling printer to create a total skin bolus made of a 5-mm-thick flexible material, which increased the skin dose through dose building. The patient's scan was segmented into upper and lower sections, with the division line placed 10 cm above the patella. The prescription was to deliver 24 Gy over 24 fractions, given 5 times per week. The plan parameters consisted of a field width of 5 cm, pitch of 0.287 and modulation factor of 3. The complete block was placed 4 cm away from the planned target region to reduce the area of the internal organs at risk, especially the bone marrow. Dose delivery accuracy was verified using point dose verification with a "Cheese" phantom (Gammex RMI, Middleton, WI), 3D plane dose verification with ArcCHECK (Model 1220, Sun Nuclear, Melbourne, FL), and multipoint film dose verification. Megavoltage computed tomography guidance was also utilized to ensure the accuracy of the setup and treatment. RESULTS: A 5-mm-thick 3D-printed suit was used as a bolus to achieve a target volume coverage of 95% of the prescribed dose. The conformity index and homogeneity index of the lower segment were slightly better than those of the upper segment. As the distance from the skin increased, the dose to the bone marrow gradually decreased, and the dose to other organs at risk remained within clinical requirements. The point dose verification deviation was less than 1%, the 3D plane dose verification was greater than 90%, and the multipoint film dose verification was less than 3%, all of which confirmed the accuracy of the delivered dose. The total treatment time was approximately 1.5 h, which included 0.5 h of wearing the 3D-printed suit and 1 h with the beam on. Patients only experienced mild fatigue, nausea or vomiting, low-grade fever, and grade III bone marrow suppression. CONCLUSION: The use of a 3D-printed suit for total skin helical tomotherapy can result in a uniform dose distribution, short treatment time, simple implementation process, good clinical outcomes, and low toxicity. This study presents an alternative treatment approach that can potentially yield improved clinical outcomes for mycosis fungoides.

Optimal threshold of a control parameter for tomotherapy respiratory tracking: A phantom study.

BACKGROUND: Radixact Synchrony® , a real-time motion tracking and compensating modality, is used for helical tomotherapy. Control parameters are used for the accurate application of irradiation. Radixact Synchrony® uses the potential difference, which is an index of the accuracy of the prediction model of target motion and is represented by a statistical prediction of the 3D distance error. Although there are several reports on Radixact Synchrony® , few have reported the appropriate settings of the potential difference threshold. PURPOSE: This study aims to determine the optimal threshold of the potential difference of Radixact Synchrony® during respiratory tumor-motion-tracking irradiation. METHODS: The relationship among the dosimetric accuracy, motion tracking accuracy, and control parameter was evaluated using a moving platform, a phantom with a basic respiratory model (the fourth power of a sinusoidal wave), and several irregular respiratory model waveforms. The dosimetric accuracy was evaluated by gamma analysis (3%, 1 mm, 10% dose threshold). The tracking accuracy was measured by the distance error of the difference between the tracked and driven positions of the phantom. The largest potential difference for 95% of treatment time was evaluated, and its correlation with the gamma-pass ratio and distance error was investigated. The optimal threshold of the potential difference was determined by receiver operating characteristic (ROC) analysis. RESULTS: A linear correlation was identified between the potential difference and the gamma-pass ratio (R = -0.704). A linear correlation was also identified between the potential difference and distance error (R = 0.827). However, as the potential difference increased, it tended to underestimate the distance error. The ROC analysis revealed that the appropriate cutoff value of the potential difference was 3.05 mm. CONCLUSION: The irradiation accuracy with motion tracking by Radixact Synchrony® could be predicted from the potential difference, and the threshold of the potential difference should be set to ∼3 mm.

Quantitative assessment of helical tomotherapy plans complexity.

PURPOSE: An unnecessary amount of complexity in radiotherapy plans affects the efficiency of the treatments, increasing the uncertainty of dose deposition and its susceptibility to anatomical changes or setup errors. To date, tools for quantitatively assessing the complexity of tomotherapy plans are still limited. In this study, new metrics were developed to characterize different aspects of helical tomotherapy (HT) plans, and their actual effectiveness was investigated. METHODS: The complexity of 464 HT plans delivered on a Radixact platform was evaluated. A new set of metrics was devised to assess beam geometry, leaf opening time (LOT) variability, and modulation over space and time. Sixty-five complexity metrics were extracted from the dataset using the newly in-house developed software library TCoMX: 29 metrics already proposed in the literature and 36 newly developed metrics. Their reciprocal relation is discussed. Their effectiveness was evaluated through correlation analyses with patient-specific quality assurance (PSQA) results. RESULTS: An inverse linear relation was found between the average number of closed leaves and the average number of MLC openings and closures as well as between the choice of the modulation factor and the discontinuity of the field, suggesting some intrinsic link between the LOT distribution and the geometrical complexity of the MLC openings. The newly proposed metrics were at least as correlated as the existing ones to the PSQA results. Metrics describing the geometrical complexity of the MLC openings showed the strongest connection to the PSQA results. Significant correlations were found between at least one of the new metrics and the γ index passing rate P R γ % ( 3 % G , 2 mm ) $P{R}_{\gamma}\%(3\%G,2\textit{mm})$ for six out of seven groups of plans considered. CONCLUSION: The new metrics proposed were shown to be effective to characterize more comprehensively the complexity of HT plans. A software library for their automatic extraction is described and made available.

Effectiveness of robust optimization against geometric uncertainties in TomoHelical planning for prostate cancer.

BACKGROUND: Geometrical uncertainties in patients can severely affect the quality of radiotherapy. PURPOSE: We evaluated the dosimetric efficacy of robust optimization for helical intensity-modulated radiotherapy (IMRT) planning in the presence of patient setup uncertainty and anatomical changes. METHODS: Two helical IMRT plans for 10 patients with localized prostate cancer were created using either minimax robust optimization (robust plan) or a conventional planning target volume (PTV) margin approach (PTV plan). Plan robustness was evaluated by creating perturbed dose plans with setup uncertainty from isocenter shifts and anatomical changes due to organ variation. The magnitudes of the geometrical uncertainties were based on the patient setup uncertainty considered during robust optimization, which was identical to the PTV margin. The homogeneity index, and target coverage (TC, defined as the V100% of the clinical target volume), and organs at risk (OAR; rectum and bladder) doses were analyzed for all nominal and perturbed plans. A statistical t-test was performed to evaluate the differences between the robust and PTV plans. RESULTS: Comparison of the nominal plans showed that the robust plans had lower OAR doses and a worse homogeneity index and TC than the PTV plans. The evaluations of robustness that considered setup errors more than the PTV margin demonstrated that the worst-case perturbed scenarios for robust plans had significantly higher TC while maintaining lower OAR doses. However, when anatomical changes were considered, improvement in TC from robust optimization was not observed in the worst-case perturbed plans. CONCLUSIONS: For helical IMRT planning in localized prostate cancer, robust optimization provides benefits over PTV margin-based planning, including better OAR sparing, and increased robustness against systematic patient-setup errors.

Verification of patient-setup accuracy using a surface imaging system with steep measurement angle.

PURPOSE: We evaluate an SGRT device (Voxelan HEV-600 M/RMS) installed with Radixact, with the view angle of the Voxelan's camera at 74 degrees. The accuracy of Voxelan with this steep angle was evaluated with phantom experiments and inter-fractional setup errors of patients. METHODS: In the phantom experiments, the difference between the measured values of Voxelan from the truth was evaluated for translations and rotations. The inter-fractional setup error between the setup using skin markers with laser localizer (laser setup: LS) and the setup using Voxelan (surface setup: SS) was compared for head and neck (N = 19), chest (N = 7) and pelvis (N = 9) cases. The inter-fractional setup error was calculated by subtracting from bone matching by megavoltage computed tomography (MVCT) as ground truth. RESULTS: From the phantom experiments, the average difference between the measured values of Voxelan from the truth was within 1 mm and 1 degree. In all cases, inter-fractional setup error based on MVCT was not significantly different between LS and SS by Welch's t-test (P > 0.05). The vector offset of the LS for head and neck, chest, and pelvis were 6.5, 9.6, and 9.6 mm, respectively, and that of the SS were 5.8, 8.6, and 12.6 mm, respectively. Slight improvement was observed for the head and neck, and chest cases, however, pelvis cases were not improved because the umbilical region could not be clearly visualized as a reference. CONCLUSION: The results show that SS in Voxelan with an installation angle of 74 degrees is equal to or better than LS.

Plan quality analysis of stereotactic ablative body radiotherapy treatment planning in liver tumor.

PURPOSE: Stereotactic ablative body radiotherapy (SABR) in the liver, RTOG-1112 guides the treatment modalities including the dose constraints for this technique but not the plan parameters. This study is not only analyzing the plan quality by utilizing the plan parameters and indexes but also compares treatment modalities from the protocol implementation. METHOD AND MATERIAL: Twenty-five patients treated in the period from February 2020 to September 2022 were recruited in this analysis. Two planners randomly selected the patients and modalities. The modalities employed were Volumetric-Modulated Arc Therapy (VMAT) and Helical Tomotherapy (HT). Various parameters and indexes were used to access not only the plan quality but also to compare each modality. The parameters and indexes studied were the homogeneity index (HI), conformity index (CI), gradient distance (GD), and the dose received by the organs at risk. RESULT: The data reveals that the mean volume of PTV is 60.8 ± 53.9 cc where these targets exhibit no significant difference between each modality. The HI shows a consistent value for both modalities. Between each modality, the CI value shows less deviation, but the HT shows slightly higher performance than VMAT. The value of GD is 1.5 ± 0.3 cm where the HT provides a shorter distance compared to VMAT as well. CONCLUSION: The parameters and indexes should be utilized for the plan evaluation although in the guidelines this was not required. Various modalities were employed for treatment. Both can achieve the treatment criteria with slightly low performance of VMAT.

Influence of different air CT numbers for IVDT on the dose distribution in TomoTherapy MVCT.

This study aims to evaluate the effect of different air computed tomography (CT) numbers of the image value density table (IVDT) on the retrospective dose calculation of head-and-neck (HN) radiotherapy using TomoTherapy megavoltage CT (MVCT) images. The CT numbers of the inside and outside air and each tissue-equivalent plug of the "Cheese" phantom were obtained from TomoTherapy MVCT. Two IVDTs with different air CT numbers were created and applied to MVCT images of the HN anthropomorphic phantom and recalculated by Planned Adaptive to verify dose distribution. We defined the recalculation dose with MVCT images using both inside and outside air of the IVDT as IVDT MVCT inair ${\mathrm{IVDT}}_{\mathrm{MVCT}}^{\mathrm{inair}}$ and IVDT MVCT outair ${\mathrm{IVDT}}_{\mathrm{MVCT}}^{\mathrm{outair}}$ , respectively. Treatment planning doses calculated on kVCT images were compared with those calculated on MVCT images using two different IVDT tables, namely, IVDT MVCT inair ${\mathrm{IVDT}}_{\mathrm{MVCT}}^{\mathrm{inair}}$ and IVDT MVCT outair ${\mathrm{IVDT}}_{\mathrm{MVCT}}^{\mathrm{outair}}$ . The difference between average MVCT numbers ±1 standard deviation on inside and outside air of the calibration phantom was 65 ± 36 HU. This difference in MVCT number of air exceeded the recommendation lung tolerance for dose calculation error of 2%. The dose differences between the planning target volume (PTV): D98% , D50% , D2% and the organ at risk (OAR): Dmax , Dmean recalculated by IVDT MVCT inair ${\mathrm{IVDT}}_{\mathrm{MVCT}}^{\mathrm{inair}}$ and IVDT MVCT outair ${\mathrm{IVDT}}_{\mathrm{MVCT}}^{\mathrm{outair}}$ using MVCT images were a maximum of 0.7% and 1.2%, respectively. Recalculated doses to the PTV and OAR with MVCT showed that IVDT MVCT outair ${\mathrm{IVDT}}_{\mathrm{MVCT}}^{\mathrm{outair}}$ was 0.5%-0.7% closer to the kVCT treatment planning dose than IVDT MVCT inair ${\mathrm{IVDT}}_{\mathrm{MVCT}}^{\mathrm{inair}}$ . This study showed that IVDT MVCT outair ${\mathrm{IVDT}}_{\mathrm{MVCT}}^{\mathrm{outair}}$ was more accurate than IVDT MVCT inair ${\mathrm{IVDT}}_{\mathrm{MVCT}}^{\mathrm{inair}}$ in recalculating the dose HN cases of MVCT using TomoTherapy.

Total Skin Treatment with Helical Arc Radiotherapy.

For widespread cutaneous lymphoma, such as mycosis fungoides or leukemia cutis, in patients with acute myeloid leukemia (AML) and for chronic myeloproliferative diseases, total skin irradiation is an efficient treatment modality for disease control. Total skin irradiation aims to homogeneously irradiate the skin of the entire body. However, the natural geometric shape and skin folding of the human body pose challenges to treatment. This article introduces treatment techniques and the evolution of total skin irradiation. Articles on total skin irradiation by helical tomotherapy and the advantages of total skin irradiation by helical tomotherapy are reviewed. Differences among each treatment technique and treatment advantages are compared. Adverse treatment effects and clinical care during irradiation and possible dose regimens are mentioned for future prospects of total skin irradiation.

Incidental Axillary Dose of Tomotherapy in Hypofractionated Whole Breast Radiotherapy for Early Breast Cancer: A Dosimetrical Analysis.

Background and Objectives: Intensity-modulated radiation therapy (IMRT) is becoming a more common method of performing whole breast irradiation (WBI) for early breast cancer. This study aimed to examine the incidental dose to the axillary region using tomotherapy, a unique form of IMRT. Patients and Methods: This study included 30 patients with early-stage breast cancer who underwent adjuvant WBI using TomoDirect IMRT. A hypofractionation scheme of 42.4 Gy delivered in 16 fractions was prescribed. The plan comprised of two parallel-opposed beams, along with two additional beams positioned anteriorly at gantry angles of 20° and 40° from the medial beam. The incidental dose received at axillary levels I, II, and III was evaluated using several dose-volume parameters. Results: The study participants had a median age of 51 years, and 60% had left-sided breast cancer. The mean dose of the axilla for levels I, II, and III were 15.5 ± 4.8 Gy, 14.9 ± 4.2 Gy, and 1.5 ± 1.6 Gy, respectively. Adequate coverage of the axilla, defined as V95%[%], was achieved for 4.7 ± 3.9%, 4.8 ± 3.7%, and 0 ± 0% for levels I, II, and III, respectively. The results were compared with those of previously published studies, and the axillary mean dose and V95%[%] of TomoDirect IMRT were low, comparable to other IMRT techniques, and lower than those of traditional tangential therapy. Conclusions: While incidental axillary radiation during WBI has been proposed to assist in regional disease control, the TomoDirect plan was demonstrated to decrease this dose, and a hypofractionation scheme would further lower its biological effectiveness. Future clinical studies should incorporate dosimetrical analysis of incidental axillary dose, in order to facilitate hypofractionated IMRT planning with risk-adjusted axilla coverage in early breast cancer.

Evolution of dosimetric treatment planning for pediatric total lymphoid irradiation (TLI): a single-institution experience.

Background: Total lymphoid irradiation (TLI) is a conditioning regimen in allogeneic hematopoietic stem cell transplantation (allo-HSCT) which may reduce long-term toxicities attributed to other techniques, such as total body irradiation (TBI). At our institution, TLI treatments were first planned with the three-dimensional conformal radiation therapy (3D-CRT) technique and later with volumetric modulated arc therapy (VMAT). With the recent availability of a basic helical tomotherapy (HT), the possible dosimetric gain of the latter for TLI is studied. Materials and methods: 22 pediatric patients were planned for VMAT and HT, prescribed to 8 Gy in 4 fractions. VMAT was planned with template based on a single cost function, using the Monaco treatment planning system (TPS). HT plans were planned using Accuray Precision TPS for a basic HT without the dynamic jaws feature or VOLO-Ultra algorithm. Plan quality was analyzed based on four quality indices, mean and maximum doses to planning target volume (PTV) and organs at risk (OARs), dose gradient and integral doses. Differences were analyzed with Wilcoxon signed-rank test. Results: HT plans resulted in improved conformity (CI) and homogeneity indices (HI) (p < 0.05) but less steep dose gradient (p = 0.181). VMAT plans created larger areas with high doses within the PTV, while comparable doses to OARs, except mainly for the spinal marrow, for which a reduction of 37.7% in D2% was obtained (p < 0.05). Integral dose for non-tumor tissue was 11.3% lower with the VMAT template (p < 0.05). Conclusion: HT achieves better conformity and homogeneity even without its more advanced features. Nevertheless, the VMAT template achieves dosimetric results close to those of HT, both with similar clinical outcome.

Comparison of helical and TomoDirect techniques with simultaneous integrated boost in early breast cancer patients.

Background: The aim of the study was to perform dosimetric comparisons of helical (H) and TomoDirect (TD) plans for whole-breast irradiation (WBI) with simultaneous integrated boost (SIB) in early-stage breast cancer patients undergoing breast conserving surgery. Materials and methods: Fifty patients, 25 with left-side and 25 with right-side tumors, were determined for a treatment planning system for a total dose of 50.4Gy in 1.8Gy per fraction to WBI, with a SIB of 2.3Gy per fraction delivered to the tumor bed. The planning target volume (PTV) doses and the conformity (CI) and homogeneity indices (HI) for PTVbreast and PTVboost, as well as organ-at-risk (OAR) doses and treatment times, were compared between the H and TD plans. Results: All plans met the PTV coverage criteria for the H plan, except for mean V107 of PTVbreast for TD plan. The H plan yielded better homogeneity and conformity of dose distribution compared to the TD plan. The ipsilateral mean lung doses were not significantly different between the two plans. The TD plans is advantageous for mean doses to the heart, contralateral breast and lung, spinal cord, and esophagus than the H plans. In both the H and TD plans, the right-sided breast patients had lower heart dose parameters than the left-sided breast patients. The TD plan is superior to the H plan in sparing the contralateral breast and lung by decreasing low-dose volumes. Conclusions: While the OAR dose advantages of TD are appealing, shorter treatment times or improved dose homogeneity and conformity for target volume may be advantageous for H plan.

Using 4D dose accumulation to calculate organ-at-risk dose deviations from motion-synchronized liver and lung tomotherapy treatments.

Tracking systems such as Radixact Synchrony change the planned delivery of radiation during treatment to follow the target. This is typically achieved without considering the location changes of organs at risk (OARs). The goal of this work was to develop a novel 4D dose accumulation framework to quantify OAR dose deviations due to the motion and tracked treatment. The framework obtains deformation information and the target motion pattern from a four-dimensional computed tomography dataset. The helical tomotherapy treatment plan is split into 10 plans and motion correction is applied separately to the jaw pattern and multi-leaf collimator (MLC) sinogram for each phase based on the location of the target in each phase. Deformable image registration (DIR) is calculated from each phase to the references phase using a commercial algorithm, and doses are accumulated according to the DIR. The effect of motion synchronization on OAR dose was analyzed for five lung and five liver subjects by comparing planned versus synchrony-accumulated dose. The motion was compensated by an average of 1.6 cm of jaw sway and by an average of 5.7% of leaf openings modified, indicating that most of the motion compensation was from jaw sway and not MLC changes. OAR dose deviations as large as 19 Gy were observed, and for all 10 cases, dose deviations greater than 7 Gy were observed. Target dose remained relatively constant (D95% within 3 Gy), confirming that motion-synchronization achieved the goal of maintaining target dose. Dose deviations provided by the framework can be leveraged during the treatment planning process by identifying cases where OAR doses may change significantly from their planned values with respect to the critical constraints. The framework is specific to synchronized helical tomotherapy treatments, but the OAR dose deviations apply to any real-time tracking technique that does not consider location changes of OARs.

Dosimetric impact of phase shifts on Radixact Synchrony tracking system with patient-specific breathing patterns.

PURPOSE: The Synchrony tracking system of Radixact is capable of real-time tumor tracking by building a correlation model between external light-emitting diodes on the patient's chest and an internal marker. A phase shift between the chest wall and a lung tumor has been reported. Hence, this study focused on evaluating the accuracy of the tracking system, especially under a patient-specific breathing pattern with respiratory phase shifts. METHODS: A phantom containing fiducial markers was placed on a moving platform. The intrinsic delivery accuracy was verified with a patient-specific breathing pattern. Three patient-specific breathing patterns were then implemented, for which phase shifts, φ, were introduced. Phase shifts with +0.3 s and +1 s were tested for dosimetric aspects, whereas ±0.3, ±0.6, and ±0.8 s shifts were used for tracking accuracy. The resultant dose distributions were analyzed by γ comparison. Dose profiles in the superior-inferior and lateral directions were compared. Logfiles of the tracking information were extracted from the system and compared with the input breathing pattern. The root mean square (RMS) difference was used to quantify the consistency. RESULTS: When the φ value was as large as 1 s, a severe inconsistency was observed. The target was significantly underdosed, down to 89% of the originally planned dose. γ analysis revealed that the failed portion was concentrated in the target region. The RMS of the tracking difference was close to 1 mm when φ was ±0.3 s and approximately 4 mm when φ was ±0.8 s. Tracking errors increased with an increase in the degree of phase shifts. CONCLUSION: Phase shifts between the patient chest wall and the internal target may hamper treatment delivery and jeopardize treatment using Synchrony Tracking. Hence, a larger planning target volume (PTV) may be necessary if a large phase shift is observed in a patient, especially when an external surrogate shows a lag in motion when compared with the tumor.